For engines close to stock tune (any size, but mild cam) full vacuum to the distributor works well.
As the cam approaches 240 degrees @ .050", full vacuum works at idle, but as you open the throttle vacuum quickly dies, which reduces RPM, etc.
Ported fixes this, since idle is based solely on initial advance it's completely stable until a later throttle position.
With a relatively small cam of 240@.050, that may be true. It's definitely not the case with my 272@.050 which idles at only 8" vacuum. Lumpy but stable with 27 degrees at idle.
The vacuum can doesn't even move at 8", but at cruise (15" Hg) it's advanced, which is exactly when the engine wants it. So it's working fine on manifold vac.
Everybody's setup is different and I agree experimenting is important.
